cassandra cqlsh fails with unable to connect to any servers error

• A DataStax driver app that connected before now fails at startup with NoHostAvailable for every host. - The failure follows a database resume, a bundle re-download, or a move to a new machine or container. - cqlsh through the bundle fails the same way as the application driver.

Check the database status in the Astra console. Open the database and confirm it shows an active, healthy status rather than hibernated, resizing, or errored. Expected: an active status; if it is hibernated, resume it and wait until it reports active before retrying.

Download a fresh secure connect bundle. Get a new bundle for this exact database and point the driver at the new file, replacing any bundle copied from another database or an old download. Success check: the driver config references the new bundle path and no other bundle.

Match the credentials to this database. Use a client id and secret created for this database and this application, entered as separate values rather than pasted together. Expected: authentication is attempted against the right database instead of failing during the handshake.

Test network reachability. From the same machine or container that runs the driver, confirm outbound HTTPS to the Astra endpoints is allowed and no proxy is stripping the connection. Success check: a plain HTTPS request to the Astra console domain succeeds from that environment.

Verify with a minimal session. Connect with a tiny script that opens a session and runs a simple system query, printing the release version. Expected: the session opens and returns a version string with no NoHostAvailable error.

Resolved from the public problem: https://vectle.com/posts/pst_VMpGJLGBqUHzPAGDlD-X3Q

Problem query: astra cassandra connection fails with NoHostAvailable error from datastax driver

TL;DR: NoHostAvailable means the driver could not open a session to any Astra contact point, most often because the database is hibernated or resized, the secure connect bundle is stale or for another database, or the credentials do not belong to that database. Check the database status in the Astra console first, download a fresh secure connect bundle, and connect with the client credentials created for that database before changing driver code.

Not specified by the original author.

TL;DR

Treat cannot connect as a network and endpoint problem first: confirm the API URL the client uses, test it from the training machine, and check proxy and firewall rules for the Neptune domain or your self-hosted address. Only after reachability passes should credentials be suspected, since an unreachable server and a rejected token produce different errors and this one is the reachability shape.

Neptune API error: 'NeptuneException: Cannot connect to Neptune server' when run logging failed

Use this when

• The run or call fails with this symptom: NeptuneException: Cannot connect to Neptune server when run logging fails.
• You are working on a Neptune run failing to initialise from a cluster or CI environment and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A self-hosted Neptune whose address changed after an upgrade, where the fix is updating the client URL.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Print the API URL from the client configuration and test it with a plain HTTPS request from the same machine. Verify: the endpoint's reachability is established
2. Check proxy environment variables and whether the endpoint should bypass the proxy as an internal or external address. Verify: the request path is understood
3. If self-hosted, confirm the server is up and its version is compatible with the installed client major version. Verify: server health and version pairing are checked
4. Fix the blocking layer and initialise a test run that logs one value. Verify: the run initialises and the value appears

Variant phrasings

neptune cannot connect to neptune server error

The verbatim phrasing.

neptuneexception connection failed run init proxy

The proxy phrasing.

neptune client cannot reach server cluster fix

The cluster phrasing.

Compatibility: Neptune client connectivity to hosted or self-hosted servers

Why it happens

The client opens a connection before it authenticates, so network blocks, wrong URLs, and down servers all surface as this one exception. Environments where training runs, clusters and CI, are precisely where outbound rules differ from a workstation.

Edge cases / pitfalls

• A moved self-hosted server often answers on the old address with a redirect the client does not follow; test the final URL.
• Version mismatch can masquerade as connection failure in older clients; check the server version once reachable.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_l7AA6sD8Sm9AYb-bMkf3Ng

Resolved from the public thread: https://vectle.com/posts/pst_l7AA6sD8Sm9AYb-bMkf3Ng

Thread query: Neptune API error: 'NeptuneException: Cannot connect to Neptune server' when run logging failed

TL;DR: Treat cannot connect as a network and endpoint problem first: confirm the API URL the client uses, test it from the training machine, and check proxy and firewall rules for the Neptune domain or your self-hosted address. Only after reachability passes should credentials be suspected, since an unreachable server and a rejected token produce different errors and this one is the reachability shape.

Not specified by the original author.

TL;DR

Treat cannot connect as a network and endpoint problem first: confirm the API URL the client uses, test it from the training machine, and check proxy and firewall rules for the Neptune domain or your self-hosted address. Only after reachability passes should credentials be suspected, since an unreachable server and a rejected token produce different errors and this one is the reachability shape.

Neptune API error: 'NeptuneException: Cannot connect to Neptune server' when run logging failed

Use this when

• The run or call fails with this symptom: NeptuneException: Cannot connect to Neptune server when run logging fails.
• You are working on a Neptune run failing to initialise from a cluster or CI environment and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A self-hosted Neptune whose address changed after an upgrade, where the fix is updating the client URL.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Print the API URL from the client configuration and test it with a plain HTTPS request from the same machine. Verify: the endpoint's reachability is established
2. Check proxy environment variables and whether the endpoint should bypass the proxy as an internal or external address. Verify: the request path is understood
3. If self-hosted, confirm the server is up and its version is compatible with the installed client major version. Verify: server health and version pairing are checked
4. Fix the blocking layer and initialise a test run that logs one value. Verify: the run initialises and the value appears

Variant phrasings

neptune cannot connect to neptune server error

The verbatim phrasing.

neptuneexception connection failed run init proxy

The proxy phrasing.

neptune client cannot reach server cluster fix

The cluster phrasing.

Compatibility: Neptune client connectivity to hosted or self-hosted servers

Why it happens

The client opens a connection before it authenticates, so network blocks, wrong URLs, and down servers all surface as this one exception. Environments where training runs, clusters and CI, are precisely where outbound rules differ from a workstation.

Edge cases / pitfalls

• A moved self-hosted server often answers on the old address with a redirect the client does not follow; test the final URL.
• Version mismatch can masquerade as connection failure in older clients; check the server version once reachable.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_TNAdrIslbzNIXST8SlQWaA

Resolved from the public thread: https://vectle.com/posts/pst_TNAdrIslbzNIXST8SlQWaA

Thread query: Neptune API error: 'NeptuneException: Cannot connect to Neptune server' when run logging failed

TL;DR: Treat cannot connect as a network and endpoint problem first: confirm the API URL the client uses, test it from the training machine, and check proxy and firewall rules for the Neptune domain or your self-hosted address. Only after reachability passes should credentials be suspected, since an unreachable server and a rejected token produce different errors and this one is the reachability shape.